The present application claims priority to British Application Serial No. GB 9925415.3, filed Oct. 28, 1999.
This invention relates to a vehicle axle and is applicable to an axle of a drive, undriven, steering or trailer system.
Conventionally, vehicle axles are built-up constructions. For example, an axle may comprise an axle beam formed as a member to which separately made side members are welded or bolted which in turn have components secured to them by fastenings or welding to provide, for example, spring seatings, trailing arms, suspension attachments and brake backplates. The member forming the axle beam may itself be of a composite construction. When the axle is a drive axle a housing of a final drive and differential assembly may be secured to the axle beam as a separate component.
The separate manufacture of component-parts and assembly into the axles makes these built-up constructions costly and time consuming to produce. Also the built-up axles can be relatively heavy.
The present invention seeks to avoid or at least reduce the amount of building up required in the production of a vehicle axle.
According to the present invention a vehicle axle is provided which comprises a member formed as a hollow monocoque structure which includes at least one integral location formed in the structure as a low stress area to receive an attachment thereto for use of the axle in a vehicle.
There may be a plurality of the integral locations formed as low stress areas in the monocoque structure to receive attachments.
The monocoque structure may be rigid or substantially so, or it may include one or more compliant portions.
The monocoque structure distributes throughout the member stresses to which the member is subjected when the axle is in use in a vehicle. Parts of the structure can be specially shaped to suit the particular stresses to which they will be subjected when the axle is in use. For example, a part which is to withstand bending forces may have its hollow cross-section extended in the direction, or main direction, in which such forces are exerted on the part. A part which needs to be torsionally compliant in use of the axle may be of angled or lobed hollow cross-section although round, oval, triangular, square or rectangular cross-sectional shapes are possible but more limited in the extent of the compliance that may be obtained. Where the structure includes an axle beam part, for example, that part is preferably of a hollow T-shaped cross-section disposed on its side for especially advantageous torsional compliance whilst providing stiffness and strength against vertical and horizontal bending forces. The hollow T-section can absorb movement under applied load but a substantial art of its torsional compliance may be provided by elastic deforming, or warping, of the section. A particular advantage which this gives is roll compliance without necessarily having to add rubber or other resilient component such as are usually relied upon in conventional axle structures. A three or more lobed cross-section may provide comparable characteristics. A round or other non-lobed cross-section, on the other hand, whilst providing compliance from strain within the material may permit little or no warping.
The wall thickness of the monocoque structure may be varied at different parts of the structure to suit the strength and/or stiffness and torsional compliance requirements of the parts.
The monocoque structure may be made of metal, for example steel, or possibly a suitable composite material. It may be formed in one piece or it may be in two or more pieces which are fixed together to provide the single structure. When formed in one piece the structure may, for example, be blown or investment cast to shape. When formed in two or more pieces, the pieces may, for example, be cast, moulded or pressed to shape and then fixed together, as by welding or bonding, into the single structure.
Preferably the structure is rounded where walls thereof meet so as to avoid sharp corners, angles or edges which might give rise to undesirable stress points.
The strength provided by the monocoque structure enables the member to be made with a wall thickness less than has generally been necessary in members which are made for the conventional built-up vehicle axles. In consequence, there can be a significant saving in weight, without loss of stiffness and strength requirements, in a vehicle axle according to the present invention over a conventional built-up axle for similar use. This is particularly advantageous in view of the general desire of vehicle manufacturers to reduce the unladen weight of vehicles. A stub axle or axles may be formed in one with the member or be a separately made component or components fixed to the member. If the axle is made as a drive axle, the rigid member may include a cavity for a drive and differential gearing assembly.
An axle in accordance with the present invention may be included in various systems. It may, for example, be included in a parallelogram structure in which it may provide a cross beam and the monocoque structure may have integrally formed in it cantilever beams above and below its central horizontal axis, as installed for use, which may, for example, have ends formed to accept welded bosses. Another example of use of the axle may be in a multilink beam axle suspension in which links are formed integrally with the monocoque structure. The axle may also be used in a trailing, semi-trailing or leading arm suspension system for which an arm or arms may be formed as an integral part of the monocoque structure. The monocoque structure may then provide a combination of axle and anti-roll functions. The or each arm may have a bush housing for a bearing formed in one with it, or a bush housing may be secured, for example by welding, to the arm. If the monocoque structure is formed with a pair of similarly directed arms it can be advantageous to have bearing bush housings made as separate components which are secured to the arms as this allows adjustment of the spacing of the bushes to suit the intended installation of the axle.
The or each integral location of the monocoque structure for an attachment may comprise, for example, a hollowed, raised or levelled portion of the structure as may be suitable for any one of various attachments for use of the axle in a vehicle.
For example, the location or locations may include: a mounting for a suspension spring or springs; anchorage for a damper and air spring unit: support for a stub axle or axles, a pivot bearing or bearings and/or for disc or drum brake mountings; a mounting or mountings for an air cylinder for a drum or disc brake; bearing for a brake camshaft; and locations for an ABS sensor and/or for attachment of brackets to receive trailing and/or leading links and/or anti-roll bars. When the axle includes arms adjacent opposite ends of an axle beam, supports for brake brackets may be provided conveniently at the juncture of the arms with the axle beam, away from the load part of the beam.
The vehicle axle may comprise more than one of the monocoque structures. Thus, for example, the axle may have one of the structures in one half of its length and another one in the other half of its length. The two structure may be connected together directly, or they may be secured to an intermediate section which may be rigid or flexible. Use of an intermediate section allows for length adjustment of the axle by selection of the size of the intermediate section rather than having to vary the size of the monocoque structures.
A vehicle axle in accordance with the present invention may be provided as original equipment in a vehicle in a vehicle, or be fitted as a replacement part in a vehicle.
According to a second aspect of the present invention a vehicle is provided which includes an axle in accordance with the first aspect of the invention as herein set forth.
An embodiment of the invention will now be described by way of example only with reference to the accompanying drawings, in which:
FIG. 1 is a top perspective view from the rear of an axle in accordance with the present invention;
FIG. 2 is an enlarged top perspective view from the rear of part of the axle, and
FIGS. 3 and 4 are respectively top and underneath perspective view from the front of part of the axle shown attached to a chassis member of a vehicle.